Pollen and Embryo Sac
The male parts of a flower consist of one or more stamens. Pollen Formation: Development Of A Pollen Grain Within The Pollen Sac Of An Anther: A cross One of the cells near to the micropyle end of the ovule is the haploid female gamete (egg cell). The most sophisticated relationships between plants and insects are. Pollen is a fine to coarse powdery substance comprising pollen grains which are male purposes; 8 See also; 9 References; 10 Bibliography; 11 External links . the placenta, guided by projections or hairs, to the micropyle of an ovule. (b) Pollen grains are visible in this single microsporophyll. (f) Within this single ovule are the megaspore mother cell (MMC), micropyle, and a pollen grain. . In a plant's male reproductive organs, development of pollen takes place in a.
The entire structure is called the embryo sac. One of the cells near to the micropyle end of the ovule is the haploid female gamete egg cell. Pollination Pollination is the transfer of pollen male gamete from the anther to a stigma.
Increases genetic variation, population more resistant to environmental change. Guarantees reproduction if pollinating agent is absent or not efficient. Pollination can be accomplished by the wind or by animals. Insects are the most common animals that will pollinate a carpel.
The most sophisticated relationships between plants and insects are generally those involving bees. Bees collect pollen and nectar not only for themselves but also to feed their young. For this reason bees have developed a number of adaptations that make them particularly good pollen carriers. These adaptations allow them to gather and carry large volumes of pollen. Bees are ideal pollinators because they visit many flowers while carrying lots of pollen, before returning to their nest.
So the chance that a bee will transfer the pollen between flowers of the same species is very high. Many insects eat pollen. In the process of eating they become covered in it.
Pollination happens when the pollen feeder transfers the pollen to the pollen receivers of the same plant, or another plant of the same species, as the insect looks for more pollen to eat.
Fertilisation Fertilisation is the union of the male and female gametes to form a zygote. Since the male and female gametes are haploid n when the two unite the zygote is diploid 2n.
Fertilisation starts when a pollen grain lands on the stigma. The pollen grain then grain germinates forming a pollen tube. The tube nucleus controls the growth of the pollen tube. The pollen tube is an example of chemotropism since it is growing toward chemicals produced from the ovule.
The generative nucleus travels down the pollen tube. It undergoes mitosis forming two haploid male gamete nuclei. The pollen tube enters the ovule by way of the micropyle.
The two male gamete nuclei are released into the embryo sac. The tube nucleus disintegrates. Double Fertilisation Since there are 2 sperm nuclei that have reached the embryo sac both nuclei will fuse with female gametes. One sperm nuclei will fuse with the egg cell to form the zygote 2n while the other sperm nucleus fuses with the 2 polar nuclei in the embryo sac to form an endosperm nucleus 3n.
Seed Formation The fertilized becomes the seed. The integuments become the wall of the seed called the testa. The endosperm nucleus leads to the formation of triploid endosperm, a food tissue. The diploid zygote, by mitosis, develops into a plant embryo. The developing embryo draws nourishment from the endosperm. The embryo ceases development and goes dormant.
Pollen - Wikipedia
The ovule becomes a seed, which contains a dormant plant embryo, food reserve, and the protective coat called the testa. The Embryo The embryo is made up of the radicle or future root and the plumule or future shoot.
The endosperm cells divide many times and absorb the nucellus. This is the nutrition mainly fats, oils and starch for the embryo.
Pollen and Embryo Sac
There are 2 types of seeds. Some are endospermic while others are non-endospermic. In endospermic seeds the food reserve is the endosperm, which is outside the plant embryo. Examples of this type of seed are maize and wheat. Non-endospermic seeds have food reserve within the cotyledon s of the plant embryo. This occurs in broad beans. Monocots and Dicots Monocots have one cotyledon in the seed while dicots have two cotyledons. The cotyledons are food reserves for the young plant after it germinates from the soil.
It uses these food reserves until it is capable of making its own food. In monocots the food is absorbed from the endosperm while in dicots the food is stored in the cotyledons. Fruit Development The ovary becomes a fruit.
32.1: Reproductive Development and Structure
The wall of the ovary becomes the wall of the fruit called the pericarp. The fruit protects the developing seeds and plays an important role in seed dispersal. This process is controlled by auxins produced by the seeds. Once the fruit forms the rest of the flower parts die and fall away.
Most late summer and fall pollen allergies are probably caused by ragweeda widespread anemophilous plant. However, as suburbs grew and people began establishing irrigated lawns and gardensmore irritating species of ragweed gained a foothold and Arizona lost its claim of freedom from hay fever. Anemophilous spring blooming plants such as oakbirchhickorypecanand early summer grasses may also induce pollen allergies. Most cultivated plants with showy flowers are entomophilous and do not cause pollen allergies.
The number of people in the United States affected by hay fever is between 20 and 40 million,  and such allergy has proven to be the most frequent allergic response in the nation. There are certain evidential suggestions pointing out hay fever and similar allergies to be of hereditary origin. Individuals who suffer from eczema or are asthmatic tend to be more susceptible to developing long-term hay fever.
Individuals carrying the ailment may at first believe that they have a simple summer cold, but hay fever becomes more evident when the apparent cold does not disappear. The confirmation of hay fever can be obtained after examination by a general physician. They do not prevent the discharge of histaminebut it has been proven that they do prevent a part of the chain reaction activated by this biogenic aminewhich considerably lowers hay fever symptoms.
Decongestants can be administered in different ways such as tablets and nasal sprays. Allergy immunotherapy AIT treatment involves administering doses of allergens to accustom the body to pollen, thereby inducing specific long-term tolerance. Discovered by Leonard Noon and John Freeman inallergy immunotherapy represents the only causative treatment for respiratory allergies.
The haploid gametophyte alternates with the diploid sporophyte during the sexual reproduction process of angiosperms. The outermost whorl of the flower has green, leafy structures known as sepals. The sepals, collectively called the calyx, help to protect the unopened bud. The second whorl is comprised of petals—usually, brightly colored—collectively called the corolla. The number of sepals and petals varies depending on whether the plant is a monocot or dicot. In monocots, petals usually number three or multiples of three; in dicots, the number of petals is four or five, or multiples of four and five.
Together, the calyx and corolla are known as the perianth. The third whorl contains the male reproductive structures and is known as the androecium. The androecium has stamens with anthers that contain the microsporangia. The innermost group of structures in the flower is the gynoecium, or the female reproductive component s. The carpel is the individual unit of the gynoecium and has a stigma, style, and ovary.
A flower may have one or multiple carpels. The four main parts of the flower are the calyx, corolla, androecium, and gynoecium. The androecium is the sum of all the male reproductive organs, and the gynoecium is the sum of the female reproductive organs. What term is used to describe an incomplete flower lacking the androecium? What term describes an incomplete flower lacking a gynoecium? If all four whorls the calyx, corolla, androecium, and gynoecium are present, the flower is described as complete.
If any of the four parts is missing, the flower is known as incomplete. Flowers that contain both an androecium and a gynoecium are called perfect, androgynous or hermaphrodites.
There are two types of incomplete flowers: The corn plant has both staminate male and carpellate female flowers. Staminate flowers, which are clustered in the tassel at the tip of the stem, produce pollen grains. Carpellate flower are clustered in the immature ears. Each strand of silk is a stigma. The corn kernels are seeds that develop on the ear after fertilization. Also shown is the lower stem and root. The a lily is a superior flower, which has the ovary above the other flower parts.
The microsporangia, which are usually bi-lobed, are pollen sacs in which the microspores develop into pollen grains. These are found in the anther, which is at the end of the stamen—the long filament that supports the anther.
Shown is a a cross section of an anther at two developmental stages. The immature anther top contains four microsporangia, or pollen sacs. Each microsporangium contains hundreds of microspore mother cells that will each give rise to four pollen grains. The tapetum supports the development and maturation of the pollen grains.
Flowering Plant Reproduction II
Upon maturation of the pollen bottomthe pollen sac walls split open and the pollen grains male gametophytes are released. An inner layer of cells, known as the tapetum, provides nutrition to the developing microspores and contributes key components to the pollen wall. Mature pollen grains contain two cells: The generative cell is contained within the larger pollen tube cell. Upon germination, the tube cell forms the pollen tube through which the generative cell migrates to enter the ovary.
During its transit inside the pollen tube, the generative cell divides to form two male gametes sperm cells. Upon maturity, the microsporangia burst, releasing the pollen grains from the anther. Pollen develops from the microspore mother cells. The mature pollen grain is composed of two cells: The pollen grain has two coverings: